Biomedical subjects

H Pohjonen

Publications and source records attributed to H Pohjonen.

8 recordsLinked to original sources

PubMed2001

PACS in Töölö hospital.

A 3-year PACS project was started in 1997 and completed in 1999 with filmless radiology and surgery. An efficient network for transferring images provides the infrastructure for integration of different distributed imaging systems and enables efficient handling of all patient-related information on one display station. Because of the need for high-speed communications and the massive amount of image data transferred in radiology, ATM (25, 155 Mbit/s) was chosen to be the main technology used. Both hardware and software redundancy of the system have been carefully planned. The size of the Dicom image library utilizing MO discs is currently 1.2 TB with 300 GB RAID capacity. For the increasing amount of teleradiologic consultations, a special Dicom gateway is planned. It allows a centralized and resilient handling and routing of received images around the hospital. Hospital-wide PACS has already improved the speed and quality of patient care by providing instant access to diagnostic information at multiple locations simultaneously. The benefits of PACS are considered from the viewpoint of the entire hospital: PACS offers a method for efficiently transporting patient-related images and reports to the referring physicians.

Finland↗

PubMed2001

Image fusion in open-architecture PACS-environment.

Multimodal digital imaging is common in many fields of diagnosis and therapy planning - there is great interest in matching globally, fusing or registering data from the same part of the body. In practice, there are still difficulties in customizing image fusion in hospitals. Efficient routine use of image fusion requires, among others, an image management infrastructure - a picture archiving and communication system (PACS) - to provide storage of image data in a standard digital format, intelligent image management and fault-tolerant high-speed image networking. In order to customize image fusion, advances in both fusion software and hardware are also needed. The algorithms should be automatic, fast and accurate enough. Registration of multimodal data also creates a need for different display techniques and user-friendly interfaces. Image fusion has been impractical and too tedious to be performed in routine work, but in the future, fused images will be used in clinical practice - even in teleradiological consultation.

Humans↗

PubMed2000

Transmission imaging for registration of ictal and interictal single-photon emission tomography, magnetic resonance imaging and electroencephalography.

A method developed for registration of ictal and interictal single-photon emission tomography (SPET), magnetic resonance imaging (MRI) and electroencephalography (EEG) is described. For SPET studies, technetium-99m ethyl cysteinate dimer (ECD) was injected intravenously while the patient was monitored on video-EEG to document the ictal or interictal state. Imaging was performed using a triple-head gamma camera equipped with a transmission imaging device using a gadolinium-153 source. The images (128x128 pixels, voxel size 3.7x3.7x3.6 mm3) were reconstructed using an iterative algorithm and postfiltered with a Wiener filter. The gold-plated silver electrodes on the patient's scalp were utilized as markers for registration of the ictal and interictal SPET images, as these metallic markers were clearly seen on the transmission images. Fitting of the marker sets was based on a non-iterative least squares method. The interictal SPET image was subtracted from the ictal image after scaling. The T1-weighted MPRAGE MR images with voxel size of 1.0x1.0x1.0 mm3 were obtained with a 1.5-T scanner. For registration of MR and subtraction SPET images, the external marker set of the ictal SPET study was fitted to the surface of the head segmented from MR images. The SPET registration was tested with a phantom experiment. Registration of ictal and interictal SPET in five patient studies resulted in a 2-mm RMS residual of the marker sets. The estimated RMS error of registration in the final result combining locations of the electrodes, subtraction SPET and MR images was 3-5 mm. In conclusion, transmission imaging can be utilized for an accurate and easily implemented registration procedure for ictal and interictal SPET, MRI and EEG.

Adolescent↗

PubMed1999

Activation of multiple cortical areas in response to somatosensory stimulation: combined magnetoencephalographic and functional magnetic resonance imaging.

We combined information from functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) to assess which cortical areas and in which temporal order show macroscopic activation after right median nerve stimulation. Five healthy subjects were studied with the two imaging modalities, which both revealed significant activation in the contra- and ipsilateral primary somatosensory cortex (SI), the contra- and ipsilateral opercular areas, the walls of the contralateral postcentral sulcus (PoCS), and the contralateral supplementary motor area (SMA). In fMRI, two separate foci of activation in the opercular cortex were discerned, one posteriorly in the parietal operculum (PO), and one anteriorly near the insula or frontal operculum (anterior operculum, AO). The activation sites from fMRI were used to constrain the solution of the inverse problem of MEG, which allowed us to construct a model of the temporal sequence of activation of the different sites. According to this model, the mean onset latency for significant activation at the contralateral SI was 20 msec (range, 17-22 msec), followed by activation of PoCS at 23 msec (range, 21-25 msec). The contralateral PO was activated at 26 msec (range, 19-32 msec) and AO at 33 msec (range, 22-51 msec). The contralateral SMA became active at 36 msec (range, 24-48 msec). The ipsilateral SI, PO, and AO became activated at 54-67 msec. We conclude that fMRI provides a useful means to constrain the inverse problem of MEG, allowing the construction of spatiotemporal models of cortical activation, which may have significant implications for the understanding of cortical network functioning.

Adult↗

PubMed1997

Accuracy of a registration procedure for brain SPET and MRI: phantom and simulation studies.

Phantom experiments and simulations were performed to evaluate the significance of different error sources in a clinical registration procedure for brain SPET and MRI based on external markers. The results from the phantom experiments were used to adjust the error model for simulations. In the phantom experiments, 13-14 external markers were attached to the surface of a three-dimensional brain phantom for computing registration. Three internal test markers were used to estimate the accuracy of registration. The phantom was imaged with two different SPET and MRI devices. The mean root-mean-squared (RMS) residual of the locations of the test markers after registration using different combinations of four external markers varied from 3.5 +/- 1.0 to 5.2 +/- 1.3 mm depending on the imaging equipment and parameters used. The accuracy improved with an increasing number of external markers, from 3.2 +/- 0.5 to 4.9 +/- 0.5 mm for 6 markers and from 3.1 +/- 0.1 to 4.7 +/- 0.1 mm for 13 markers. In simulations, the external markers had an error comparable to the corresponding error in the phantom experiments. The error in the test markers was varied independently of that of the external markers. When the locating error of the test markers was removed, about 2 mm of the residuals of the test markers were found to come from this source. When an error comparable to the resolution of the original images (7-10 mm for SPET, 2 mm for MRI) was included in the test markers, the largest mean RMS residual after registration was smaller than the resolution error (8.8 +/- 1.1 mm). This was due to the accuracy of localization of the external markers and the fact that the direction of the error was random for each marker. The size of the registration error of an image volume was site-dependent, being minimal near the centre of mass of the external markers. When comparing the error with the spatial resolution of SPET, it was concluded that the accuracy of registration is not the limiting factor in region-of-interest analysis of registered images, provided that the design and attachment of the marker system are appropriate.

Brain↗

PubMed1996

Registration and display of brain SPECT and MRI using external markers.

Accurate anatomical localisation of abnormalities observed in brain perfusion single-photon emission computed tomography (SPECT) is difficult, but can be improved by correlating data from SPECT and other tomographic imaging modalities. For this purpose we have developed software to register, analyse and display 99mTc-hexamethylpropyleneamine oxime SPECT and 1.0 T MRI of the brain. For registration of SPECT and MRI data external skin markers containing 99mTc (220 kBq) in 50 microliters of coconut butter were used. The software is coded in the C programming language, and the X Window system and the OSF/Motif standards are used for graphics and definition of the user interface. The registration algorithm follows a noniterative least-squares method using singular value decomposition of a 3 x 3 covariance matrix. After registration, the image slices of both data sets are shown at identical tomographic levels. The registration error in phantom studies was on average 4 mm. In the two-dimensional display mode the orthogonal cross-sections of the data sets are displayed side by side. In the three-dimensional mode MRI data are displayed as a surface-shaded 3 D reconstruction and SPECT data as cut planes. The usefulness of this method is demonstrated in patients with cerebral infarcts, brain tumour, herpes simplex encephalitis and epilepsy.

Brain↗

PubMed1995

Segmentation methods for volume determination with 111In/99Tcm SPET.

Objective determination of regions of interest (ROIs) is a prerequisite for the accurate quantification of radionuclide volume distributions in single photon emission tomographic (SPET) images. In this study, we compared four segmentation methods: fixed thresholding (FT), grey level histogram (GL), region growing (RG) and combined region growing and edge detection (RGE). For this purpose, an elliptical phantom containing two cylinders with varying volumes (8-360 ml) and activities of 111In and 99Tcm (2.9-37 kBq ml-1) was employed. Using these methods, the following correlation was observed between true and measured phantom volumes: 111In, r = 0.95 (FT), 0.73 (GL), 0.93 (RG) and 0.92 (RGE); 99Tcm, r = 0.85 (FT), 0.72 (GL), 0.85 (RG) and 0.89 (RGE). Volume determination with FT and RG was not sensitive to the cut-off frequency used in image filtering. A significant correlation was observed between spleen volumes measured with the different segmentation methods, except GL, when applied to the SPET images of 25 patients administered 111In-labelled platelets. On the basis of these results, FT and RG are recommended for the clinical determination of ROIs, although they can be difficult to apply if the signal-to-noise ratio is very low or highly variable, when a combination of different imaging modalities may be the only accurate solution to the segmentation problem. The RGE method can also produce accurate results, but estimation of parameters is laborious with this method. Before being applied clinically, all segmentation methods tested in this study require phantom measurements for the determination of optimal parameters.

Humans↗

PubMed1994

Quality assurance of the bedside chest radiography process.

The bedside chest radiography process was analyzed in terms of modern quality management guidelines and the sources of quality problems were identified. In order to analyze systematically the various quality factors, the process was described in a top-down fashion with the aid of data flow diagrams. Two internal quality control points and one external point were found in the process. Means to measure quality at the quality control points including questionnaires and a formula for calculating the internal quality index were developed.

Humans↗